Head mounted display devices used for example in augmented reality environments often use active illuminated cameras for 3D sensing and ranging. Such cameras may employ one or more illumination assemblies for emitting pulsed light, and a light sensor for receiving the laser light reflected back from objects within the field of view of the camera. The distance to the objects within the field of view may then be determined, using for example time of flight or structured light methods. The one or more laser diodes and light sensor are encased behind a visor or other optical shield used for aesthetics and to protect the components of the head mounted display device including the one or more laser diodes and light sensor.
A problem with conventional head mounted display device designs is that light from the one or more illumination assemblies may be disrupted by the visor and coupled to the light sensor, thereby distorting depth camera measurements. This may happen two ways. First, some portion of the light from a laser diode may be reflected by the visor directly back into the light sensor according to Fresnel's Equations. Second, contaminants on one or both surfaces of the visor, or imperfections in the surface coatings of the visor may cause some portion of the light from a laser diode to couple into the visor. This phenomenon, referred to herein as waveguiding, transmits the light from the laser diode through the visor and into the light sensor.